NAIROBI, Kenya (CNN) -- Running battles erupted across Kenya on Wednesday after the country's opposition leader called for three days of nationwide protests against the outcome of last month's presidential elections.

Police shot three protesters in Kibera, a slum on the outskirts of Nairobi, a witness told CNN, and other officers fired tear gas to try to thwart thousands of protesters.

Journalists were caught up in the melee, including CNN's Zain Verjee, who was hit in the back with a tear gas canister as she reported outside Nairobi's Uhuru Park, where the opposition planned a protest rally.

Police and paramilitary forces encircled the park, a common rallying point for the opposition, and held the protest marchers and journalists at bay with the tear gas.

Officers and paramilitary forces were out in force around Kibera and in other parts of the Kenyan capital. They also patrolled the western town of Kisumu, in the Rift Valley, where many shops were closed in anticipation of violence.

The tense day followed the election Tuesday of an opposition candidate as house speaker in a contentious session of parliament full of angry accusations and heckling.

Opposition party candidate Kenneth Marende was elected speaker in the third round of voting, winning 105-101 over the government's candidate, Francis Ole Kaparo, who had been speaker since 1993.

Another opposition lawmaker, Farah Maalim, was later elected deputy speaker.

The votes marked a significant win for opposition leader Raila Odinga, who was in the chamber for the vote. He refused to look at President Mwai Kibaki as the president entered.

It was the first session of parliament since the disputed presidential and parliamentary elections last month. Kibaki says voters re-elected him, but Odinga has contested that result.

International election monitors have said the election was flawed.

Residents interviewed on the streets of the capital didn't appear to look forward to Odinga's call for protests.

"Mass action is not a good idea," one man said.

"Me personally, I'm afraid," said one woman.

The opposition said it wants to use peaceful street protests to pressure the government to come to some sort of genuine power-sharing deal with Odinga. It accuses Kenyan police of provoking the violence, but police say they must keep control of the crowds so that they don't become unruly and lead to further unrest.

The outcome of the December 27 election sparked widespread and ethnically motivated violence in which more than 600 people were killed and thousands of others were displaced.

Supporters of Kibaki, a member of the Kikuyu tribe, battled with supporters of Odinga, a member of the Luo tribe, in bloody street battles that often involved machetes. And Kenya, long one of the most stable and economically developed nations in East Africa, descended into chaos.

Odinga said that, despite the violence, he would be prepared in a new government to work with, but not under, Kibaki. He called on the president to negotiate on power-sharing and to set a date for new elections.

Former U.N. Secretary-General Kofi Annan had planned to arrive in Kenya on Tuesday to mediate the dispute, but he postponed the effort for a couple of days because he was hit with the flu, his office said. It said Annan will try to make the trip as soon as possible.E-mail to a friend